One part is the dimensions of the image in in pixels. A good size for posting is up to about 800 pixels wide and maybe a little less vertically. For example a image that is 600 pixels high and 800 pixels wide would fit well on most computer screens. There is no limit on the dimensions that can be posted and the dimensions of the image are not directly related to the file size.

The other important part of the image is the file size and this is limited to 200 kb (kilobytes)for posting here. If you view a photo on your computer or online you should be able to right click on the photo and select Properties or View Image Info to see the photo dimensions and the file size.

If your image file size or quality is too large (over the 200 kb limit) you can use a photo editor to reduce the file size or there are many options if you do a Goggle search for photo resizing.